The present invention relates to a method for determining geometric data for vehicle parking processes.
It is believed that driver assistance systems will be used to an increasing extent in future generations of vehicles. Parking assistance systems are already widespread in which the distance from obstacles in the front and/or rear area of the vehicle when parking is measured by ultrasonic sensors and the driver receives an audible indication.
A method of determining the length of a parking gap between a vehicle parked in front and one parked behind is disclosed in German Patent Document Number DE 196 16 447 A1. An ultrasonic or radar transceiver is installed in the vehicle to be parked to measure the length of the parking gap. As the vehicle to be parked drives slowly past the parked vehicles, the position of the vehicle to be parked is determined in the driving direction relative to the front end of the vehicle parked behind, and from this position the distance of the car parked in front from the vehicle to be parked is determined. The distance between the two parked vehicles, i.e., the length of the parking space, is determined from the measurements. It is also mentioned that it can be useful to measure and take into account the lateral distance of the moving vehicle to the vehicle parked behind in order to determine the position of the moving vehicle relative to the front end of the vehicle behind. The details of how this is performed are not provided in the aforementioned patent document.
The object of the present invention is to provide a method by which, as exact as possible, geometric data relevant to parking processes can be ascertained at the lowest possible technological expense.
This object is achieved by a method for determining geometric data for parking processes for vehicles, wherein the lateral distance between the vehicle and a curb is measured at least twice successively, by a vehicle-affixed distance sensor as the vehicle is driven alongside the parking space, and the angle between the longitudinal axis of a vehicle and the curb is determined, by the acts of: determining an angle of sideways movement between the present longitudinal direction of the vehicle and a preset longitudinal direction, which angle results from the sideways movement of the vehicle as it is driven by; determining a curb angle between the preset longitudinal direction and the curb resulting from the course of the contour of the curb; and determining the angle between the present longitudinal axis of the vehicle and the curb by adding the sideways movement angle and the curb angle.
In accordance with exemplary embodiments of the present invention, geometric data for a vehicle to be parked, which is moving alongside a parking space or parking gap, which are relevant to a parking process or an electronically controlled parking process is determined. The geometric data can include the angle between the longitudinal axis of the vehicle and the curb, as soon as it can be derived, the distance between a sensor point on the vehicle and the curb, i.e., the distance between the vehicle and the curb, and the effective length of the parking space or gap.
The present invention takes into account the sideways movement of the vehicle to be parked “sideways to the parking space or sideways to the parking gap” when determining the angle between the longitudinal axis of the vehicle and the curb. To determine the angle between the longitudinal axis of the vehicle and the curb, a distance sensor is provided on the vehicle, for example an ultrasonic, radar or laser sensor, with which the lateral distance is measured between the vehicle or, more precisely, between the sensor point on the vehicle, and the curb.
According to the present invention, the angle between the longitudinal axis of the vehicle and the curb is the sum of a “angle of sideways movement” and an “angle of the curb”. During the parking process, drivers often do not drive by the parking gap in an exactly parallel manner. Instead, the drivers often turn briefly in the direction of the parking gap in the first third or the middle of the parking gap and then drives forward at an angle to a stop before backing into the parking gap. Depending on the steering behavior of the driver, the vehicle to be parked thereby makes a certain sideways movement when passing the parking gap. “Angle of sideways movement” is understood hereinafter to mean the angle between the present longitudinal direction of the vehicle when moving past the parking space or gap and a “preset longitudinal direction”. The “preset longitudinal direction” is understood to mean, for example, the direction in which the vehicle is moving before beginning to turn in, i.e., before a “change in course”. The preset longitudinal direction can quite generally be understood to mean the direction in which the vehicle is moving when going in a straight line. The preset longitudinal direction may essentially be parallel to the curb.
Sometimes the vehicle is moving in a straight line, but diagonally to the curb. The curb is then not parallel to the selected preset longitudinal direction. The angle between the preset longitudinal direction and the curb is hereinafter called the “curb angle”. The angle sought between the longitudinal axis of the vehicle and the curb is the sum of the angle of sideways movement and the curb angle.
According to an aspect of the present invention, the angle of sideways movement is determined from a “path relationship”, i.e., from a “sideways movement distance component” and the path covered by the vehicle between two measurement points when being driven alongside the parking space or gap. The “sideways movement distance component” is the sideways movement of the sensor point of the vehicle in relation to the preset longitudinal direction. The sideways movement distance component is determined by measuring the path covered by the vehicle when moving alongside the parking space between two measurement points and the steering position controlled by the driver, i.e., the steering angle on the steering column or the steering angle of the steered wheels. The sideways movement distance component can be determined from the path covered between two measurement points and the steering position by a preset mathematical vehicle model and trigonometric conversion. The angle of sideways movement is determined from this by further simple trigonometric conversion.
To determine the curb angle, the difference of two distance measurements between the sensor point on the vehicle and the curb is determined. The previously determined sideways movement distance component is then subtracted from this difference. The resulting difference is hereinafter called the “curb distance component”. The curb distance component can be interpreted as the “angularity” of the curb relative to the preset logitudinal direction taken as the basis. The curb angle can be determined by trigonometric conversion from the curb distance component and the path covered by the vehicle when moving alongside the parking space or gap. As already mentioned, the curb angle is the present angle between the preset longitudinal direction and the curb.
The curb angle and the angle of sideways movement are then added, to provide the angle sought between the longitudinal direction of the vehicle and the curb.
The “division” of the angle between the longitudinal axis of the vehicle and the curb into an angle of sideways movement and a curb angle has very substantial advantages in terms of the accuracy of measurement attainable over a direct determination of the angle sought from two consecutive distance measurements.
The angle of sideways movement can be determined with great precision with relatively few problems. This requires only a sufficiently accurate vehicle model, the path covered by the vehicle between two measurement points which can, for example, be determined via ABS sensors, and the steering position of the vehicle which can, for example, be measured by steering angle sensors on the steerable wheels or on the steering column.
Determining the curb angle as precisely as possible is much more problematic. For this purpose, the distance must be determined between the distance sensor attached to the vehicle and the curb. This distance measurement can be faulty due to various distorting factors. Measurement errors can be caused, for example, by curved curbstones, stones on the roadway, manhole covers or objects lying on the roadway.
To “smooth out” measurement errors in determining the curb angle, it is therefore desirable to take distance measurements at short intervals of, for example, 2.5 cm as seen in the direction in which the vehicle is moving. In this way, a large number of measurements are taken. By repeating the procedure described above to determine curb angles, several curb angles are obtained from which a mean value, i.e., a mean curb angle, can be formed. This mean value can largely eliminate different outliers and produce a sufficiently precise result for the curb angle.
Another highly essential parameter for automatic control or regulation of a parking process is the present distance of the vehicle from the curb, or more precisely, the distance of a vehicle-affixed sensor point from the curb.
In theory, the distance could be determined by a simple measurement of distance. As already explained, various measurement errors may occur in this process. Consequently it is difficult to assess the accuracy of individual measurements. In the extreme case, individual measurements may be completely unusable. Therefore, it is advantageous to determine a “mean distance”.
According to an aspect of the present invention, the method includes making successive several distance measurements between the vehicle affixed sensor point and the curb as the vehicle moves by the parking gap. The “sideways movement distance component” and the “curb distance component” explained above are each subtracted from the distances measured. A mean value is then formed from the values obtained.
Accordingly, the sideways movement distance component and the curb distance component are each calculated from the individual distance measurements; A mean value is formed from the values obtained. The present distance of the vehicle-affixed sensor from the curb is then obtained by adding the mean values obtained to the previously calculated sideways movement distance components and the curb distance components. Accordingly, the actual present distance of the vehicle-affixed sensor from the curb can be determined with great accuracy. The larger the number of distance measurements entering into the calculation, the more errors are “smoothed out”.
Another essential parameter for automating parking processes is the effective length of the parking gap. As already explained, as they drive by a parking gap, many drivers steer briefly into the parking gap and then drive forward again at an angle, stop and back into the parking gap. The path covered by the vehicle in the area of the parking gap is therefore curved and thus longer than the effective length of the parking gap. With the procedure described above, the angle between the longitudinal axis of the vehicle and the curb can be determined at a large number of measurement points as the vehicle moves past the parking gap. According to an aspect of the present invention, the effective parking gap length is obtained by projecting the vehicle trajectory, i.e., of the path covered by the vehicle, onto the curb.
Thus the effective parking gap length can be determined mathematically at measurement intervals by trigonometric conversion from the path covered by the vehicle and the angle between the longitudinal axis of the vehicle and the curb at the individual measurement intervals.
The front and rear end of a parking gap can be determined by measuring in the following manner. When the vehicle to be parked is driven by the parking gap, there is a positive jump in the distance measurement signal as the distance sensor passes the rear end of the parking gap. The distance from the curb detected by the distance sensor therefore increases “abruptly”. Correspondingly the distance measured makes a negative jump if the distance sensor passes the front end of the parking gap.
In order to eliminate distortions or to smooth out measurement errors, several successively measured measurement signals can also be taken into account when the front and rear end of a parking gap are determined. For example, the end of a parking gap is only acknowledged when a preset minimum number of measurements deviates by more than a preset value from the previous mean distance.